Filtration system and method

ABSTRACT

Described are multi-stage drum filtration systems including a primary rotary drum filter stage, at least one passive filter stage, and a main fan configured to create a vacuum on an inlet side of the primary rotary drum filter stage. The multi-stage drum filtration system may also include a HEPA filter stage. A controller may be configured to control a speed of the main fan to maintain an inlet vacuum to the primary rotary drum filter stage that corresponds to an inlet vacuum set point input.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is continuation of U.S. patent application Ser. No.14/060,574, filed Oct. 22, 2013, entitled FILTRATION SYSTEM AND METHOD,which is a divisional of U.S. patent application Ser. No. 13/445,767,filed on Apr. 12, 2012, entitled FILTRATION SYSTEM AND METHOD, nowissued as U.S. Pat. No. 8,597,391, which is related to and claimspriority benefits from U.S. Provisional Application Ser. No. 61/517,004,filed on Apr. 12, 2011, entitled FILTRATION SYSTEM AND METHOD. The '004'767 and '574 applications are hereby incorporated in their entiretiesby this reference.

FIELD OF THE INVENTION

The field of the invention relates in general to a rotary drumfiltration system. More specifically to a multi-stage drum filter thatreduces the amount of particulates that remain airborne in the filterduring operation, and that uses passive-only filters after the drumfilter section.

BACKGROUND

The main absorbent part of most disposable sanitary products ordisposable diapers is the pad, or core. The pad is often made of woodpulp that has been fiberized by a special mill, designed to handlefluffing pulp. In the past, this pad was usually made of wood pulp. Now,it is more common that the pad is made of some combination of wood pulpand absorbent polymer. After the pulp is fiberized, the resulting pulpfluff is drawn out of the mill onto a forming screen. The pad is formedon the screen in a forming chamber, in which the pulp fluff and polymeris placed on the forming screen and is forced into a compactconfiguration by suction of air through the screen. After the pad isformed on the screen, it moves through a set of profiling rolls and onto the folding and packaging part of the converting machine.

The air that is pulled through the forming screen from the pulp millcontains small amounts of fiberized pulp fluff and, in many cases,absorbent polymer. Experience has shown that the amount of the wastefluff and/or polymer that comes through the forming screen is 2% or 3%of the total amount of fluff and/or polymer that enters the formingchamber.

Several filters have been developed for filtering the waste particulatesout of the air exiting the forming chamber. These filters have severaladvantages. First, the filters clean the air that comes from the formingscreen and return the air to the plant area or vent the air outside ofthe plant.

Second, the waste particulates that come through the forming screen arerecovered and returned to the mill or forming chamber. The recoveredparticulates that are returned to the process represent a substantialcost savings to the manufacturer.

For uniform pad formation to take place in the forming chamber, thevolume of air moving through the forming chamber and the pressure ofthat air should be consistent. If the air volume or pressure is changed,the pad will have different thicknesses and absorbencies and may notmeet specification. By assisting in moving air through the formingscreen, a properly-constructed filter can help to assure air volume andair pressure consistency through the forming chamber.

One of the filters that is used for removing the waste pulp particulatesfrom the air that moves through the forming screen is the rotary drumvariety, such as is depicted in FIG. 1. In many cases, when the aircontains large quantities of waste particulates, conventional rotarydrum filters, when used as a first stage filter, quickly become loadedand undergo severe drops in efficiency. In these cases, the air mayfirst pass through a pre-separator, such as a cyclone, condenser, etc.,to remove larger and/or heavier particulates prior to the rotary drumfilter stage.

As can be seen in FIG. 1, the process air from the forming chamber ofthe production machine with the waste particulates entrained are fedthrough a conduit 12 into a drum filter enclosure 14. The conduit 12 mayfeed the air and entrained waste particulates to the filter enclosure 14from the top as shown or may deposit the air and entrained wasteparticulates from the forming chamber at an opening along the bottom ofthe filter enclosure 14. A rotary drum 16, which includes a filtrationmedia 18 along its outside, rotates within the drum filter enclosure 14.One end of the rotary drum 16 is closed off (not shown in FIG. 1). Theother end of the drum opens to a compartment (not shown in FIG. 1) whichhouses one or more clean air, or main, fans for withdrawing the air fromthe filter enclosure 14. The main fan (not shown in FIG. 1) is used topull air through the filtration media 18 and then through the open endof the drum 16.

As the drum 16 rotates and as the clean air is pulled through the medium18, particulates 19 settle on the filtration media 18. Theseparticulates 19 are vacuumed off the filtration media 18 through asuction nozzle 20 by a purge fan 22. This fan 22 and another conduit 24then route the particulates 19 back to the production line and/or to anoffline collection system for disposal. The clean air, which is pulledthrough the filtration media 18 by the fans of the system, is returnedto the plant area or is exhausted outside the plant.

The clean air fan, or main fan, is used at the open end of the rotarydrum filter for pulling the particulates onto forming screen, pullingthe waste particulates to the filter enclosure, and pulling the wasteparticulates onto the filtration media 18 of the drum filter. Inaddition, a material handling fan may be used to move the forming airand particulates from the mill through the forming chamber. The materialhandling fan, also known as a forming fan, is located on the conduit 12extending from the forming chamber to the drum filter.

The drum filter enclosure generally can only handle approximately 12inches water column (wc) of negative pressure. The material handling fanmust be used if the forming chamber requires more than 8 inches we ofnegative pressure. If a material handling fan is used in the formingchamber, then the fan at the rear end of the drum filter, or the cleanair fan, is used as a balancing fan to keep the filter under a negativepressure. Because increasing forming chamber pressure is a commonrequirement of sanitary products machine manufacturers, materialhandling fans are often used to generate the required high pressures andvolumes in a system. In such systems, the clean air fan located at theend of the rotary drum filter serves mainly as a balancing fan to keepthe filter under negative pressure.

One of the problems found in the rotary drum filter systems is thatwaste particulates 19 have a tendency to accumulate in bottom corners 26of the filter enclosure 14. Because of gravity, the waste particulates19 have a tendency to remain in these corner areas. Further particulates19 stick to the accumulated particulates, and the problem is compounded.Manufacturers are often forced to shut down the line and clean out thisparticulate accumulation.

One manner of avoiding particulate accumulation in the corners 26 is byproviding a baffle 28 in the corner of the enclosure to decrease thearea in which particulates 19 can accumulate. Another method ofpreventing some of the particulate accumulation utilizes placement ofthe conduit 12 at the bottom of the enclosure 14. In this manner, aturbulent blast of air is created at the bottom of the filter enclosure,which somewhat prevents the accumulation of particulates 19 on the floorin places in direct contact with the turbulent air stream. At least onemanufacturer has utilized more than one inlet across the bottom of thechamber in order to create an even more turbulent air flow. However, ithas been found that this solution, even when used with a baffle, doesnot adequately solve the particulate accumulation problem.

Particulate accumulation can cause other problems in a filter systemother than noncleanliness. The particulates 19 within the enclosure canact as fuel for a fire, or “explosion.” Manufacturers have set limitsfor the amount of particulates 19 per unit volume that they consider asafe amount to be in the enclosure 14 at a given time. This limit isoften referred to as the “lower explosion limit,” or “LEL,” and variesamong different manufacturers. The limit is also referred to as the“lower flammability limit (“LFL”).” Calculation of the limit may or maynot include the particulates 19 located on the outside of the filtrationmedia 18. However, regardless of the limit set, the particulates 19accumulated at the bottom of the enclosure 14 and at the corners 26 ofthe enclosure is included in the calculation.

To prevent any possible explosions in a filter enclosure from spreadingto other parts of a plant, manufacturers often provide explosion vents(not shown) at the top of the enclosure 14. The explosion vents openwhen a certain pressure is built up within the enclosure 14. The ventprovides an escape for igniting gases, and prevents an explosion fromspreading to all parts of a plant. The explosion vent typically leads toa duct, which is vented to the outside of the plant. The duct usuallyleads from the explosion vent at the top of the enclosure up to andthrough the roof of the manufacturer's facility. The structure andinstallation of the explosion vent and its duct work can often be moreelaborate and more expensive than the filter enclosure 14. Thus,manufacturers have searched for ways to avoid having to provide theseexplosion vents.

In some cases, it is necessary to add additional filter stages after theprimary rotary drum filter stage to achieve the required air puritylevel. A multi-stage drum filter may be used in these cases. The typeand quantity of additional filter stages can vary. Examples of filterstages include self-cleaning filter stages and passive filter stages. Aself-cleaning filter is usually a filter that has an automatic methodfor cleaning itself without operator intervention. A passive filtertypically refers to any filter that does not have self-cleaningcapabilities, and usually refers to a pocket or bag filter. Oneadvantage of passive filters is the ability to capture particulateswithin the pockets or bags, which keeps the particulates out of theairstream. As a result, the level of particulates are more easilymaintained below the LEL, which helps minimize the risk of explosion inthe passive filter stages. Passive filters are typically less expensivethan self-cleaning filters because they do not require any type ofautomated self-cleaning machinery, but may not be feasible for use inprocesses where the air leaving the primary rotary drum filter stage hashigh concentrations of dust because the passive filters may becomeclogged quickly and require frequent maintenance and/or replacement.

As a result, for processes with relatively high dust concentrationsremaining in the air following the rotary drum filter stage, aself-cleaning filter stage is commonly used after the primary rotarydrum filter stage because the periods between maintenance events isoften longer for a self-cleaning filter than for a passive filter inthis type of environment.

The most common types of self-cleaning filters used for the filter stageafter the primary rotary drum filter stage are cartridge final filtersor disk filters. Cartridge final filters use a bank of cartridge filtersthat are periodically cleaned with a burst of compressed air. Thiscompressed air cleaning is controlled by a control panel, which isactivated based on the amount of pressure drop across the cartridges.When the pressure drop across the cartridges reaches a certain level,which has been set to indicate that the cartridges are dirty, thecompressed air cleaning cycle is automatically initiated. However, whenthe compressed air cleaning cycle is initiated, the particulates areblown away from the cartridges and re-entrained into the air. As aresult, it is difficult to control the level of particulates below theLEL with the cartridge final filters, which can increase the risk ofexplosion in the self-cleaning filter stages.

A disk filter is typically a secondary rotary drum filter stage that ispositioned after the primary rotary drum filter stage. This secondaryrotary drum filter stage is often shorter in length than the primaryrotary drum filter stage, but the operational principles and featuresare the same as those for the primary rotary drum filter stage.

Therefore, in order to minimize costs and maximize efficiency of themulti-stage drum filter system, as well as avoiding the potentialexplosion risks that may be introduced by cartridge final filters, it isdesirable to have a passive filter located in the second stage after theprimary rotary drum filter stage, instead of a self-cleaning filter. Asa result, it may be desirable to improve the efficiency of the primarydrum filter stage so that the air leaving this stage has a lowerconcentration of dust that must be processed by the passive filters. Itis also desirable to improve the performance of the primary rotary drumfilter stage so that a pre-separator stage prior to the rotary drumfilter stage is not required. Alternatively and/or additionally, it maybe desirable to improve the holding capacity of the passive filters inthe second stage so that the periods between maintenance and/orreplacement are extended.

SUMMARY

Various embodiments of the invention relate to a multi-stage drumfiltration system comprising a primary rotary drum filter stage, atleast one passive filter stage coupled to an outlet side of the primaryrotary drum filter stage, and a main fan coupled to the stages andconfigured to create a vacuum on an inlet side of the primary rotarydrum filter stage. The multi-stage drum filtration system may furthercomprise a second passive filter stage. The multi-stage drum filtrationsystem may further comprise a HEPA filter stage coupled to an outletside of the at least one passive filter stage.

In certain embodiments, the multi-stage drum filtration system may alsofurther comprise a pressure sensor positioned adjacent the inlet side ofthe primary rotary drum filter stage, and a controller connected to thepressure sensor and the main fan and configured to receive input fromthe pressure sensor and transmit a speed signal to the main fan. Thecontroller may be configured to control a speed of the main fan tomaintain an inlet vacuum to the primary rotary drum filter stage thatcorresponds to an inlet vacuum set point input. A variable frequencydrive may be connected to the main fan, wherein the variable frequencydrive receives the speed signal from the controller, converts the speedsignal into a new speed signal, and transmits the new speed signal tothe main fan.

The primary rotary drum filter stage may comprise a rotary drum andfiltration media. In some embodiments, the filtration media isconfigured to achieve a pressure differential between 0.5-1.5 inches at100 ft/min face velocity when the filtration media is clean and between1.0-4.0 inches at 100 ft/min face velocity when the filtration media 122is loaded. A seal may be positioned between an open end of the rotarydrum and an enclosure wall between the primary rotary drum filter stageand the first passive filter stage, wherein the seal may comprise anon-overlapping seam, and wherein the seal is held in position adjacentthe enclosure wall via a mechanical stop.

The at least one passive filter stage may comprise a plurality ofindividual filters, wherein each individual filter may comprise aminimum filter efficiency of at least MERV 8 per ASHRAE 52.2. Likewise,the second passive filter stage comprises a plurality of individualfilters, wherein each individual filter may comprise a minimum filterefficiency of at least MERV 8 per ASHRAE 52.2. Finally, the HEPA filterstage comprises a plurality of individual filters, wherein eachindividual filter is rated for 2000 CFM at 1.4 inches water gauge(“w.g.”).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a prior art rotary drum filter, with part ofthe enclosure removed.

FIG. 2 is a perspective view of a multi-stage drum filtration systemaccording to certain embodiments of the present invention.

FIG. 3 is a partial perspective view of a rotary drum and suctionnozzles used in conjunction with the multi-stage drum filtration systemof FIG. 2.

FIG. 4 is a photograph showing a side view of filtration media used inconjunction with the multi-stage drum filtration system of FIG. 2.

FIG. 5 is a front perspective view of an open end of a rotary drum usedin conjunction with the multi-stage drum filtration system of FIG. 2.

FIG. 6 is a perspective view of a purge fan used in conjunction with themulti-stage drum filtration system of FIG. 2.

FIG. 7 is a perspective view of an inlet side of a first passive filterstage used in conjunction with the multi-stage drum filtration system ofFIG. 2.

FIG. 8 is a perspective view of an outlet side of the first passivefilter stage of FIG. 7.

FIG. 9 are perspective and close-up views of a filter used inconjunction with the first passive filter stage of FIG. 7.

FIG. 10 is a perspective view of an inlet side of a second passivefilter stage used in conjunction with the multi-stage drum filtrationsystem of FIG. 2.

FIG. 11 is a perspective view of an outlet side of the second passivefilter stage of FIG. 10.

FIG. 12 are perspective and close-up views of a filter used inconjunction with the second passive filter stage of FIG. 10.

FIG. 13 is a perspective view of an inlet side of a HEPA filter stageused in conjunction with the multi-stage drum filtration system of FIG.2.

FIG. 14 is a perspective view of an outlet side of the HEPA filter stageof FIG. 13.

FIG. 15 are perspective and close-up views of a filter used inconjunction with the HEPA filter stage of FIG. 13.

FIG. 16 is a perspective view of a main fan used in conjunction with themulti-stage drum filtration system of FIG. 2.

FIG. 17 is a simplified flow diagram illustrating a system forcontrolling inlet pressure of a multi-stage drum filtration systemaccording to certain embodiments of the present invention.

FIG. 18 is diagram of a control system apparatus of a multi-stage drumfiltration system according to certain embodiments of the presentinvention.

DETAILED DESCRIPTION

Embodiments of the invention provide a multi-stage drum filtrationsystem and method of use. While the multi-stage drum filtration systemand method of use are discussed for use with fiberized particulates,they are by no means so limited. Rather, embodiments of the multi-stagedrum filtration system may be used with any type of manufacturing systemthat generates any type of particulates that need to be removed andreclaimed from process air or otherwise as desired.

FIGS. 2-18 illustrate embodiments of a multi-stage drum filtrationsystem 100. In some embodiments, the filtration system 100 may comprisea primary rotary drum filter stage 102, a first passive filter stage104, a second passive filter stage 106, and/or a HEPA filter stage 108.

In these embodiments, as best illustrated in FIGS. 2-3, the primaryrotary drum filter stage 102 may comprise a rotary drum 110 and a filterenclosure 112 that is coupled to the manufacturing process. In theseembodiments, the primary rotary drum filter stage 102 may be the firstfiltration stage of the multi-stage drum filtration system 100, suchthat the process air does not pass through a pre-separator or other typefilter prior to entering the primary rotary drum filter stage 102. Theprocess air containing the particulates may be fed through a conduit 114into a forming fan 116. The forming fan 116 may be used to help move theair and particulates from the manufacturing process through a formingchamber and into the filter enclosure 112.

In these embodiments, the forming fan 116 may be configured to blow theair and particulates through a conduit 118, herein referred to as aforming fan transition 118, into the filter enclosure 112 at a pointnear a floor 120 of the filter enclosure 112. The floor 120 may becurved, or concave, and extend at least a portion of the way up one sideof the filter enclosure 112 opposite the forming fan transition 118.

In some embodiments, the rotary drum 110 may have a diameter rangingfrom 4 feet to 10 feet, but may have other suitable diameters as neededdepending on the volume of air and the concentration of particulates tobe removed. The rotary drum 110 typically rotates within the filterenclosure 112 at speeds ranging from 4 to 6 RPM, but may rotate at otherspeeds as needed depending on the volume of air that is flowing into thefilter enclosure 112 and the concentration of particulates within theair.

In some embodiments, as shown in FIGS. 2-4, the rotary drum 110 iscovered with a filtration media 122. The filtration media 122 most oftenused is a knit material that has a woven acrylic backing, and polyesterfibers. A side view of the edge of an embodiment of the filtration media122 is shown in FIG. 4. However, one of skill in the relevant art willunderstand that any suitable materials may be used to form thefiltration media 122 that achieves a pressure differential that rangesbetween 0.5″ and 1.5″ at 100 ft/min face velocity when the filtrationmedia 122 is new, to 1.0″ to 4.0″ at 100 ft/min face velocity when thefiltration media 122 is dirty (loaded).

In these embodiments, the filtration media 122 is more efficient atremoving dust from the airstream than conventional filtration media usedin combination with the rotary drum 110. This higher efficiency has beenachieved primarily by increasing the density of fibers in the filtrationmedia 122. The density of the filtration media 122 in these embodimentsis 4 oz per square foot, whereas conventional filtration media typicallyaverage 2.6 oz per square foot. The filtration media 122 in theseembodiments is available in pile heights that range from ½″ to 1″. Theminimum efficiency rating of the filtration media 122, per ASHRAEstandard 52.2, is at least MERV 8, and may be at least MERV 10, butfiltration media 122 with a higher MERV rating may also be used.

In some embodiments, as best illustrated in FIGS. 2-3, 5, and 16, afirst end 124 of the rotary drum 110 may be closed off, and a second end126 may be to a fan duct 128 leading to a balancing, or main fan 130,and/or additional filter stages 104, 106, and/or 108. The main fan 130may be configured to move air through the second end 126 of the rotarydrum 110 and therefore through the filtration media 122 in theseembodiments. The rotary drum 110 may be rotated by a drive motor 132, asshown in FIG. 2.

In some embodiments, as best illustrated in FIG. 3, the primary rotarydrum filter stage 102 may include a seal 134 between the rotary drum 110and a stationary enclosure wall 136, which is the wall located adjacentthe second end 126 of the rotary drum 110. The seal 134 reduces theamount of dust that leaks past the primary rotary drum filter stage 102.In some embodiments, the seal 134 may be formed of composite materials,fabric, and rubber-based materials, but other similar suitable materialsmay also be used. In some embodiments, the seal 134 may comprisemultiple layers of materials that are positioned over one another and/ormay be integrally formed or adhered to one another. The seal 134 may beheld in place by a mechanical stop 137, which is positioned to hold theseal 134 in place adjacent the stationary enclosure wall 136.

In certain embodiments, a non-overlapping seam (i.e., a butt seam) maybe used to form the seal 134, wherein ends of the seal 134 are placed incontact with one another without any overlap. The ends of the seal 134may be joined via any suitable mechanical or chemical fasteners,including but not limited to adhesives, adhesion welding, splice tape,or other suitable mechanisms. This type of joint allows the seal 134 tomaintain a consistent thickness along its circumference, which mayresult in a tighter seal between the primary rotary drum filter stage102 and the first passive filter stage 104. In other embodiments, theseal 134 may be continuous so that no seam is included along itscircumference. In yet other embodiments, an overlapping seam may be usedto form the seal 134, wherein one end of the seal 134 is positioned overanother end of the seal 134 so that the two ends are in overlappingcontact. The two overlapping ends of the seal 134 may be joined via anysuitable mechanical or chemical fasteners, including but not limited toadhesives, adhesion welding, splice tape, or other suitable mechanisms.One of ordinary skill in the relevant art will understand that anysuitable seal may be used between the rotary drum 110 and the stationaryenclosure wall 136 that limits the amount of dust that leaks past theprimary rotary drum filter stage 102.

In some embodiments, as illustrated in FIGS. 2-3 and 6, at least onesuction nozzle 138 is located along one side of the rotary drum 110 forremoving the particulates as they accumulate on the surface of thefiltration media 122. In some embodiments, a plurality of suctionnozzles 138 may be used with the primary rotary drum filter stage 102.However, one of ordinary skill in the relevant art will understand thatany suitable suction nozzles 138 or other similar devices, in anylocation or combination, may be used to remove the particulates from thesurface of the filtration media 122. In these embodiments, a returnconduit 139 may lead from the suction nozzles 138 to a nozzle suctionfan 140, or purge fan 140. The purge fan 140 and another conduit 142 maybe configured to route the recovered particulates back to themanufacturing process. The rating of the purge fan 140 should be sizedproperly to overcome the increased density of the filtration media 122.It is desirable for the purge fan 140 to generate at least −35″ ofvacuum pressure at the suction nozzle 138 inlet for filter cleaning.

The design of the forming fan transition 118 and the rounded floor 120of the filter enclosure 112, as well as the process for removingparticulates from the filter enclosure 112 are described in detail inU.S. Pat. No. 5,679,136, the entire contents of which are incorporatedherein by reference.

In some embodiments, the primary rotary drum filter stage 102 serves asthe first stage of removing particulates from the air. Once the air haspassed through the filtration media 122 and exited the second end 126 ofthe rotary drum 110, the air then passes through one or more passivefilter stages 104, 106 and/or the HEPA filter stage 108.

In some embodiments, as shown in FIGS. 2 and 7-8, the first passivefilter stage 104 comprises a bank 144 of multiple individual pocketfilters 146. In these embodiments, the air may enter the first passivefilter stage 104 via an inlet side 148 of the first passive filter stage104, as illustrated in FIG. 7, and exit via an outlet side 150 of thefirst passive filter stage 104, as illustrated in FIG. 8. In someembodiments, each individual filter 146 may have a configuration asshown in FIG. 9, wherein each filter 146 is 24″×24″×26″ deep, but mayhave other suitable dimensions as needed to provide sufficientfiltration and particulate removal of the airstream exiting the primaryrotary drum filter stage 102. In certain embodiments, the minimum filterefficiency, per ASHRAE 52.2, is at least MERV 8, and may be at leastMERV 10. However, one of ordinary skill in the relevant art willunderstand that filters with different MERV ratings can be used whennecessary. Each filter 146 may be rated for at least 2000 CFM, but othersuitable ratings may be used as needed. The quantity of filters 146required in the filter bank 144 is calculated from the total airflowvolume through the primary rotary drum filter stage 102.

In these embodiments, as illustrated in FIG. 9, pocket filters 146 maybe used that have depth-loading characteristics that enable each filter146 to hold more dust than the pocket filters that are traditionallyused. One of ordinary skill in the relevant art will understand that anysuitable passive filter may be used in this stage that provides thedesired particulate removal and capacity to efficiently handle the levelof dust concentration leaving the primary rotary drum filter stage 102.

In some embodiments, as shown in FIGS. 2 and 10-11, once the air haspassed through the first passive filter stage 104 and exited the outletside 150, the air may then pass through the second passive filter stage106. In these embodiments, the air may enter the second passive filterstage 106 via an inlet side 152 of the second passive filter stage 106,as illustrated in FIG. 10, and exit via an outlet side 154 of the secondpassive filter stage 106, as illustrated in FIG. 11. In someembodiments, the second passive filter stage 106 comprises a bank 156 ofmultiple individual pocket filters 158. Each individual filter 158 mayhave a configuration as shown in FIG. 12, wherein each filter 158 is24″×24″×26″ deep, but may have other suitable dimensions as needed toprovide sufficient filtration and particulate removal of the airstreamexiting the first passive filter stage 104. In certain embodiments, theminimum filter efficiency, per ASHRAE 52.2, is at least MERV 8, and maybe at least MERV 14. However, one of ordinary skill in the relevant artwill understand that filters with different MERV ratings can be usedwhen necessary. Each filter 158 may be rated for at least 2000 CFM, butother suitable ratings may be used as needed. The quantity of filters158 required in the filter bank 156 is calculated from the total airflowvolume through the primary rotary drum filter stage 102.

In these embodiments, as illustrated in FIG. 12, the pocket filters 158may have depth-loading characteristics that enable each filter 158 tohold more dust than the pocket filters that are traditionally used. Oneof ordinary skill in the relevant art will understand that any suitablepassive filter may be used in this stage that provides the desiredparticulate removal and capacity to efficiently handle the level of dustconcentration leaving the first passive filter stage 104.

In some embodiments, as shown in FIGS. 2 and 13-14, once the air haspassed through the second passive filter stage 106 and exited the outletside 154, the air quality may be such that the air can be freelyreleased into the plant, the air may then pass through additionalpassive filter stages, as described above with respect to the firstand/or second passive filter stages, and/or the air may then passthrough an optional HEPA filter stage 108. In these embodiments, the airmay enter the HEPA filter stage 108 via an inlet side 160 of the HEPAfilter stage 108, as illustrated in FIG. 13, and exit via an outlet side162 of the HEPA filter stage 108, as illustrated in FIG. 14. In someembodiments, the HEPA filter section 108 comprises a bank 164 ofmultiple individual HEPA filters 166. Each individual HEPA filter 166may have a configuration as shown in FIG. 15, wherein each filter 166 is24″×24″×11.5″ deep, but may have other suitable dimensions as needed toprovide sufficient filtration and particulate removal of the airstreamexiting the second passive filter stage 106. Each filter 166 may berated for at least 2000 CFM@1.4 inches w.g., but other suitable ratingsmay be used as needed. The quantity of HEPA filters 166 required in thefilter bank 164 is calculated from the total airflow volume through theprimary rotary drum filter stage 102.

In these embodiments, as illustrated in FIG. 15, the HEPA filters 166may have characteristics that enable each filter 166 to capture 99.97%of all particles down to 0.3 micron. One of ordinary skill in therelevant art will understand that any suitable HEPA filter may be usedin this stage that provides the desired particulate removal and capacityto efficiently handle the level of dust concentration leaving the secondpassive filter stage 106.

In certain embodiments, once the air has passed through the HEPA filterstage 108 and exited the outlet side 162, the air quality may be suchthat the air can be freely released into the plant. Depending on theconcentration of dust and the volume of air entering the multi-stagedrum filtration system 100, additional passive and/or self-cleaningstages may be added or removed from the system 100 as needed to achievethe desired level of air quality exiting the system 100.

According to certain embodiments, the level of vacuum throughout thesystem 100 may be controlled via a control system 200. FIG. 17 is asimplified flow diagram illustrating a system 200 for controlling inletpressure of a multi-stage drum filtration system according to certainembodiments of the invention. The control system 200 may includeprocessing logic that may comprise hardware (circuitry, dedicated logic,etc.), software (such as is run on a general purpose computing system ora dedicated machine), firmware (embedded software), or any combinationthereof.

Referring to FIG. 17, the control system 200 may be configured tocontrol the inlet pressure of the primary rotary drum filter stage 102by monitoring the vacuum level at the inlet of the primary rotary drumfilter stage 102, as illustrated in step 220-240, and adjusting thespeed of the main fan 130, as illustrated in steps 250-270, to hold theinlet vacuum at a desired set point (step 210). As the primary rotarydrum filter stage 102 becomes dirty (loaded) and experiences anincreased pressure drop across it, the control system 200 automaticallyadjusts by increasing the speed of the main fan 130 to generate theadditional vacuum required through the primary rotary drum filter stage102. By controlling the inlet vacuum, the primary rotary drum filterstage 102 may be operated with a lower vacuum level on the clean side ofthe primary rotary drum filter stage 102, thereby reducing the amount ofdust and particulates that are pulled through the filtration media 122.

To understand the benefit of the control system 200 on the process, itis helpful to first understand how a typical rotary drum filtrationsystem operates without the control system 200. In such a process, thevacuum level of the main fan 130 is held constant (at −12″ wetypically), and the vacuum level at the inlet to the primary rotary drumfilter stage 102 varies depending on the relative cleanliness ordirtiness of each successive filter stage 104, 106, and/or 108. In mostapplications, the result is that the primary rotary drum filter stage102 inlet vacuum level ranges from between −9″ wc when all of the filterstages are clean, to −3″ wc when all of the filters stages are dirty.This inlet vacuum fluctuation occurs slowly, and it typically takesseveral months to cover the full range. The downside to this controlscheme is that there is a higher than necessary vacuum in the clean sideof the primary rotary drum filter stage 102. The main fan 130 is sizedfor the worst case pressure drop (when all filter stages are dirty), butoperates at this rating all of the time, even when the filter stages areclean. As a result, this higher vacuum pulls more dust particles throughthe seal 134 and the filtration media 122 than an optimized vacuum levelwould.

In the embodiments that utilize the control system 200 to adjust thevacuum level, at step 210, an operator enters the desired inlet vacuumset point into a control panel 320. If there is not a human machineinterface (“HMI”) on the control panel 320, then the operator enters thevalue directly into a controller 330 (such as a smart relay or PLC)inside the control panel 320. The recommended inlet set point forstandard applications is −2″ to −3″ wc, but other suitable vacuum setpoints may be used as needed depending on variations in machinery,materials, throughput, etc.

At step 220, the control system 200 detects the inlet vacuum measurementof the primary rotary drum filter stage 102. The amount of inlet vacuummay be measured with a pressure sensor 345 mounted to the filterenclosure 112 near the inlet to the primary rotary drum filter stage102. One of ordinary skill in the relevant art will understand that anysuitable device may be used that is configured to monitor vacuum levelsand provide that information to the control system 200. The pressuresensor 345 generates a 4-20 ma signal based on the vacuum measurementdetected inside the filter enclosure 112.

At step 230, a controller 330 (such as a smart relay or PLC) inside thecontrol panel 320 receives the 4-20 ma signal from the pressure sensor345. This signal is converted to a numeric value representing the vacuumlevel, and this value is compared against the set point value. At step240, the controller 330 decides whether the inlet vacuum measurementmatches the set point value. If so, no adjustment is required to thespeed of the main fan 130 and the control system 200 proceeds to back tostep 220. If the two values do not match, then at step 250, thecontroller 330 calculates the new speed requirement for the main fan130.

At step 260, the controller 330 outputs a 4-20 ma speed signal to avariable frequency drive (“VFD”) 335, which may be used to vary thespeed of the direct drive main fan 130 to achieve the required vacuumrating. At step 270, the VFD 335 converts this 4-20 ma signal andoutputs the required speed signal (Hz) to the main fan 130. In someembodiments, the VFD 335 may be programmed with a maximum allowablespeed output that is intended to maintain the amount of vacuum withinthe range needed for the particular filter design. In this embodiment,the maximum speed output is based on the fan curve of the main fan 130,and is typically selected so that the maximum static pressure the mainfan 130 can generate is −12″ wc.

FIG. 18 is a diagram of a control system apparatus 300 of a multi-stagedrum filtration system according to certain embodiments of the presentinvention. The various participants and elements in the control system200 may use any suitable number of subsystems in the control systemapparatus 300 to facilitate the functions described herein. Examples ofsuch subsystems or components are shown in FIG. 18. The subsystems orcomponents shown in FIG. 18 may be interconnected via a system bus 310or other suitable connection. In addition to the subsystems describedabove, additional subsystems such as a printer 365, keyboard 380, fixeddisk 375 (or other memory comprising computer-readable media), monitor355, which is coupled to a display adaptor 360, and others are shown.Peripherals and input/output (I/O) devices (not shown), which couple tothe controller 330, can be connected to the control system 200 by anynumber of means known in the art, such as a serial port 370. Forexample, the serial port 370 or an external interface 385 may be used toconnect the control system apparatus 300 to a wide area network such asthe Internet, a mouse input device, or a scanner. The interconnectionvia the system bus 310 allows the central processor 350 to communicatewith each subsystem and to control the execution of instructions from asystem memory 325 or the fixed disk 375, as well as the exchange ofinformation between subsystems. The system memory 325 and/or the fixeddisk 375 may embody a computer-readable medium.

The software components or functions described in this application maybe implemented via programming logic controllers (“PLCs”), such as AllenBradley ControlLogix, Siemens S7, or other suitable PLCs. These PLCs mayuse any suitable PLC programming language, such as Allen Bradley RSLinx, Siemens SIMATIC WinCC, or other suitable PLC programming language.One of ordinary skill in the relevant art will understand that anysuitable PLC and/or PLC programming language may be used. In otherembodiments, the software components or functions described in thisapplication may be implemented as software code to be executed by one ormore processors using any suitable computer language such as, forexample, Java, C++ or Perl using, for example, conventional orobject-oriented techniques. The software code may be stored as a seriesof instructions, or commands on a computer-readable medium, such as arandom access memory (RAM), a read-only memory (ROM), a magnetic mediumsuch as a hard-drive or a floppy disk, or an optical medium such as aCD-ROM. Any such computer-readable medium may also reside on or within asingle computational apparatus, and may be present on or withindifferent computational apparatuses within a system or network.

The invention can be implemented in the form of control logic insoftware or hardware or a combination of both. The control logic may bestored in an information storage medium as a plurality of instructionsadapted to direct an information processing device to perform a set ofsteps disclosed in embodiments of the invention. Based on the disclosureand teachings provided herein, a person of ordinary skill in the artwill appreciate other ways and/or methods to implement the invention.

In embodiments, any of the entities described herein may be embodied bya computer that performs any or all of the functions and stepsdisclosed.

Any recitation of “a”, “an” or “the” is intended to mean “one or more”unless specifically indicated to the contrary.

While this invention has been described in detail with particularreference to preferred embodiments thereof, it will be understood thatvariations and modifications can be affected within the spirit and scopeof the invention as described hereinbefore and as defined in theappended claims. For example, the filter enclosure 112 may be used inany industry or application in which fiberized particulate or dust is tobe separated from conveying air. Also, it is possible to run the system100 without the forming fan 116, as long as the main fan 130 canmaintain the filter enclosure 112 at a desired negative pressure, and anadequate air flow from the processing line to the main fan 130 may bemaintained.

The foregoing is provided for purposes of illustrating, explaining, anddescribing embodiments of the present invention. Further modificationsand adaptations to these embodiments will be apparent to those skilledin the art and may be made without departing from the scope or spirit ofthe invention.

That which is claimed is:
 1. A multi-stage drum filtration systemcomprising: (a) a primary rotary drum filter stage comprising a rotarydrum and filtration media, wherein the filtration media is configured toachieve a pressure differential between 0.5-1.5 inches at 100 ft/minface velocity when the filtration media is clean and between 1.0-4.0inches at 100 ft/min face velocity when the filtration media is loaded;(b) at least two passive filter stages coupled to an outlet side of theprimary rotary drum filter stage; (c) a main fan coupled to the stagesand configured to create a vacuum on an inlet side of the primary rotarydrum filter stage; (d) a pressure sensor configured to monitor inletpressure to the primary rotary drum filter stage; and (e) a controllerconnected to the pressure sensor and the main fan and configured tocontrol a speed of the main fan to maintain the inlet pressure to theprimary rotary drum filter stage at a pre-set level.
 2. The multi-stagedrum filtration system of claim 1, further comprising a HEPA filterstage coupled to an outlet side of the at least two passive filterstages.
 3. The multi-stage drum filtration system of claim 2, whereinthe HEPA filter stage comprises a plurality of individual filters, eachindividual filter comprising a rating of 2000 CFM at 1.4 inches w.g. 4.The multi-stage drum filtration system of claim 1, further comprising avariable frequency drive connected to the main fan, wherein the variablefrequency drive receives a speed signal from the controller, convertsthe speed signal into a new speed signal, and transmits the new speedsignal to the main fan.
 5. The multi-stage drum filtration system ofclaim 1, further comprising a seal positioned between an open end of therotary drum and an enclosure wall between the primary rotary drum filterstage and the at least two passive filter stages.